Triggered by the report of the drowsy driving on the Shinkansen in 2003, sleep apnea syndrome (SAS) has rapidly attracted a great deal of attention in recent years. SAS is a disease in which such a symptom that respiration stops (apnea state) for at least 10 seconds or the respiratory tract is narrowed to thin the respiration while the patient sleeps, more specifically, the amount of ventilation lowers (hypopnea state) by at least 50% for at least 10 seconds is repeated at least five times an hour on the average. Symptoms such as a headache in getting up and drowsiness in the daytime appear in the SAS patient. SAS also causes hypertension, and it is said that the rate of complication of a myocardial infarction, cerebral apoplexy and the like rises in the SAS patient. In addition, symptoms such as nycturia, impotence, heaviness in the head and hydrodipsia may also appear. While SAS is frequently observed among middle-aged and elderly males, it is said that the same has been on the increase also among children in recent years. While the cause therefor is unknown, it is also said that the same is the fate of the human race getting to so frequently ingest soft food that the chin begins to degenerate.
It is said that the number of SAS patients is about 4% of the total population, i.e., 4.8 million in number in Japan, and it is also said that the number of potential patients thereamong is 2.8 million. An SAS patient tends to cause a traffic accident or an industrial accident by drowsy driving. It is extremely dangerous for an SAS patient to work as the driver of public transport such as an electric train, and an immediate countermeasure is required.
In the meantime, SAS is mainly diagnosed by precise diagnosis with a polysomnogram test (PSG test) at present, and a simple method omitting partial items of the PSG test, such as a simple test employing a pulse oximeter or a respiratory frequency (respiration rate) measurer, for example, is utilized as a screening method. While the subject can be tested with a portable apparatus and may not be hospitalized but can be tested also at home in the simple test, the PSG test is necessary for definition of the diagnosis. In the diagnosis with the PSG, however, hospitalization is regarded as necessary. Further, analysis by a technician is necessary after the test, and labor, time and high cost have been required. In the PSG test or the simple test, in addition, a measuring tool such as a thermistor is arranged around the mouth or the nose of the subject, and hence the same has disturbed a natural sleep.
On the other hand, a method of examining the presence or absence of respiration through a body motion resulting from respiration has also been developed. For example, a method employing a specific mat for catching a change in the height of the mat resulting from respiration as a change in the air pressure has been put into practice. However, this method is inferior in SN ratio. In other words, this method is a technique of determining the change from specific mathematical signal analysis in order to distinguish a body motion resulting from a pulse or turning over while sleeping in bed and a body motion resulting from respiration from each other, and has been inferior in reliability. Further, an apparatus for detecting the change in the air pressure must be incorporated into the mat, and hence the structure is complicated, and manufacturing thereof has also been intricate.
Under such circumstances, an optical fiber sheet prepared by fixing or mixing optical fiber to or into a sheet or the like made of cloth or the like is disclosed in Japanese Patent Laying-Open No. 2007-61306. This optical fiber sheet catches a shape change in the optical fiber caused by a body motion as a change in a polarization state of light propagating in the optical fiber. In a case of employing this optical fiber sheet, there are such advantages that the SN ratio is excellent, a slight body motion such as respiration can be detected, turning over while sleeping in bed or a pulse and respiration can be clearly distinguished from each other, and the state of respiration can be observed in a state close to an ordinary living environment.